Lipid refers to a substance that has a long-chain fatty acid or similar hydrocarbon chain in a molecule and that is present in an organ or derived from a zoic organ. The lipid can be classified into simple lipid and complex lipid. The simple lipid is composed of C, H and O and is generally soluble in acetone, and triacylglycerol as a simple lipid is present as an energy reservoir in a fat tissue of an animal body. On the other hand, the complex lipid is a group of lipid containing P of phosphoric acid, N of a baser etc. Therefore, the complex lipid is composed of a hydrophobic part (fatty acid part) and a hydrophilic part (phosphoric acid and base parts) and exhibits amphophilic nature. Generally, the above simple lipid is soluble in acetone, while the complex lipid is insoluble in acetone. Such complex lipid is a constituent of a biomembrane.
The above complex lipid can be classified into (1) glycerophospholipid [which phosphatidylcholine (alias lecithin), phosphatidylethanolamine, etc., belong to], (2) sphingophospholipid (which sphingomyelin, ceramide ciliatine, etc., belong to), (3) sphingoglycolipid (which cerebroside, sulfatide, ganglioside, etc., belong to) and (4) glyceroglycolipid (which includes lipids in which various saccharides bond to diacyl glycerol existing in mirorganism or higher plant). The above (2) sphingophospholipid and (3) sphingoglycolipid are generically referred to as “sphingolipid”.
The above glycerophospholipid is a generic term for lipids having glycerophosphoric acid backbone in their structure, and includes phosphatidylcholine (lecithin), phosphatidylethanolamine, diphosphatidylglycerol, etc. Many lipids belonging to this glycerophospholipid are those in which the non-polar portion is a fatty acid ester, while some are of a plasmalogen-form having a vinyl ether bond.
The above glycerophospholid is important as a constituent of biomembrane, and above all, the plasmalogen-form glycerophospholipid has high radical sensitivity by its vinyl-ether bond and is hence in recent years highlighted as a phospholipid having anti-oxidation nature. It is recently reported that the plasmalogen-form glycerophospholipid contributes to oxidation-stability of phospholipid membrane containing cholesterol through a mechanism different from the counterpart of α-tocopherol that is an anti-oxidation constituent of cell membrane (for example, see “J. Lipid Res.”, Vol. 44, pages 164-171 (2003)). Further, it is also pointed out that the plasmalogen-form glycerophospholipid not only takes part in the oxidation resistance of cell membrane and lipoprotein, but also has an important role in the information communication system of cells (for example, see “J. Mol. Neurosci.”, Vol. 16, pages 263-272; discussion pages 279-284 (2001)).
The above plasmalogen-form glycerophospholipid is expected to have the function of preventing the death of brain nerve cells in dementia. Under the circumstances, however, there is found no safe supply source that is safe and makes a large amount available.
On the other hand, the sphingoiipid is a generic term for lipids having a long-chain base such as sphingosine, and it is composed mainly of sphingoglycolipid and sphlngophospholipid as described already. The sphingoglycolipid contains a long-chain base such as sphingosine or fat sphingosine in addition to saccharide and long-chain fatty acid. The simplest sphingoglycolipid is cerebroside, and it includes sulfatide in which a sulfuric acid group is bonded thereto, ceramide oligohexoside in which several molecules of neutral saccharide are bonded, ganglioside in which sialic acid is bonded, etc. These lipids are present in cell cortex and are thought to take part in a recognitive mechanism.
The sphingophospholipid is classified into a derivative of ceramide 1-phosphoric acid and a derivative of ceramide 1-phosphonic acid. As the former, sphingomyeline is well known, and as the latter, ceramide ciliatine (ceramide aminoethylphosphonic acid).
These sphingolipids are spotlighted since it has been shown in recent years that ceramide, sphingosine, sphingosine-1-phosphoric acid, etc., which are decomposition metabolites thereof, take part in the information communication in cells. Further, the sphingolipids take part in the formation of a membrane microdomain called “raft” together with cholesterol, etc., and it has been shown that this microdomain plays an important role as a site of information communication, so that more and more attention has been paid thereto.
These sphingolipids have been conventionally extracted from cow brains and utilized, while those which are derived from cereals or fungi are now used from a safety standpoint. Since, however, sphingold bases constituting sphingolipids derived from cereals or fungi differ from those of mammals, there is a problem that their utility in organisms is low as compared with human-form sphingolipids.
Meanwhile, when a relatively large amount of sphingomyelin is produced from total lipids of foods, animal tissues, etc., it is produced by eluting it stepwise by means of column chromatography using silicic acid, etc., or by fractionating it stepwise according to a solvent fractionation method. Both of these require complicated procedures. In the solvent fractionation method, it is general practice to employ a method in which acetone is added to total lipids to precipitate complex lipid (phospholipid) (insoluble portion), the insoluble portion is washed with ether to remove glycerophospholipid, and the residue is taken as a sphingolipid fraction. This fraction contains not only sphlngomyelin but also glycerosphingolipids such as cerebroside.
On the other hand, it is known that the phospholipid of chicken-skin contains much human-form spingomylelin and plasmalogen-form glycerophospholipid.